1. Technical Field
The present invention relates to monitoring data, and in some embodiments may concern assessing the medical condition of a patient. More particularly, some examples of the invention concern using a subcutaneous sensor to measure a characteristic of tissue in a patient, and in some examples may be used to measure tissue pH to detect shock, or to determine if tissue is viable.
2. Description of Related Art
Improved casualty/patient care is vital to military operational practices, and is also of great importance in many civilian environments. For example, frequently it is important for a medical care provider to be able to quickly and accurately assess the medical condition of a patient in a combat environment, during disaster relief, at an accident scene, during patient transport, in an emergency room, at a hospital, or at any other location during a medical emergency or the general treatment of a patient.
Shock is one of the body's biochemical reactions to an injury. The presence of hypoglycemic or hemorrhagic shock, which frequently occurs in combat casualties and accident victims, must be rapidly and accurately assessed, and must be monitored, to ensure the best prognosis, final patient disposition, and maximum survival rates.
Detecting depression of a patient's vital signs (blood pressure, respiration and heart rate), is a known method for detecting shock. This technique may be used in the field and other environments. However, this method is imprecise and is not favored if other methods are available.
Two methods are known that generally have been used for monitoring the shock state of a patient in a hospital environment. In the first method, global blood flow assessments are made by measuring arterial Pa(O2) oxygen delivery to the body. In the second method, arterial blood lactate concentrations and oxygen consumption are measured. Both of these techniques are invasive and hence may negatively impact the patient's health, because they generally require drawing blood with a catheter (perhaps from the stomach), and also require sophisticated equipment, and consequently cannot be used in the field.
Tissue tonometry is a tissue oriented approach to measuring and diagnosing the shock state of a patient. Tissue P(O2) levels, tissue P(CO2) levels, and tissue pH, have been shown to be reliable estimates of a compensated shock state. However, the use of these approaches has been hampered by the lack of a reliable and noninvasive method of obtaining accurate measurements.
In combat, disaster, and accident scenarios, the extent of injury to a patient may be so severe as to require amputation of gangrenous tissue. Gangrenous tissue is tissue that has died due to lack of blood supply. Dead tissue may also be present on frostbite victims. Generally, the goal of an amputation is to remove all dead tissue. The extent of tissue removal during an amputation may be excessive, because medical personnel lack an accurate means of determining the demarcation between viable and non-viable tissue.
In summary, known methods of measuring the shock state of a patient are inadequate because they are invasive, non-portable, and/or inaccurate. Further, known methods for identifying and monitoring the border between viable and non-viable tissue are not sufficiently accurate to preclude needless amputation of viable tissue. Additionally, there is no known means of monitoring the continued viability of tissue after an amputation.